A machine apparatus such as a machine tool for which high accuracy positioning is required involves the problem of degradation of the accuracy of control due to friction. Particularly, a reciprocating motion such as a movement starting again after a stoppage is subject to friction, and there is the possibility of an increase in a position deviation that corresponds to a deviation between a position command and the position of a load shaft. Thus, performed is a control that compensates for friction produced in the machine apparatus.
As a friction compensation method for the machine apparatus of the related art, there is a method that experimentally adjusts in advance the amount of correction and the timings of the correction start and the correction end for friction and adds the amount of correction to a speed command and to a torque command. However, in this method, properties of friction change temporally or differ according to drive conditions or for each machine apparatus, thereby requiring time for the adjustment.
As another friction compensation method, there is a method that estimates a friction force of the machine apparatus using a friction model and compensates for an actual friction force on the basis of the estimated friction force. Types of friction compensation methods that use friction models include a feedforward type that estimates a friction force from a position command or a control command such as a target value and a feedback type that estimates a friction force from an actual position or a speed.
The friction compensation methods that use friction models provide simpler adjustment than the above method that uses the amount of correction, provided that the accuracy of estimation of a friction force is high.
As an example, in PTL 1, there is disclosed a motor control device that controls a motor using feedback control, the device including a disturbance torque observer that estimates a disturbance torque of the motor in order to reduce influence of disturbance due to friction upon reversal of the motor, in which an output value of the disturbance torque observer is controlled by a variable gain upon other than the reversal of the motor.